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refresh

The refresh attribute enables data sources for visual elements to be periodically reloaded from a server. Its value is an integer representing the number of seconds between reloads.

Supporting Tags

The refresh attribute is supported by the <data> tag. If the attribute is omitted, the data source specified in the <data> tag will only load once, when the document is parsed for the first time.

Examples

<data src="http://www/cgi-bin/MesoData.acgi$latest.mdf"
  param="TAIR" units="fahr" refresh="60"/>
         
<data src="199902011315.mdf" param="RELH" refresh="300"/>

Notes

Although the refresh attribute is specified in seconds, the current implementation limits reloads to one-minute intervals. This limit was put in place to reduce the potential for overloading our web servers.

By definition, a refresh rate of "0" means that a data source will not be refreshed after its initial loading.

In many cases, several elements within the same map or graph will specify the same data source, and it is possible that they will specify different refresh rates for the same source. In these cases, the software will reload the data source as specified by the smallest refresh rate, but it will only update elements according to their own refresh rates. The WxML example below illustrates this behavior:

<WxML>
  <map>
  
    <contour>
      <data src="http://www/mesodata.cgi?latest.mdf"
        param="TAIR" refresh="60"/>
    </contour>
         
    <contour>
      <data src="http://www/mesodata.cgi?latest.mdf"
        param="TDEW" refresh="300"/>
    </contour>
         
    <observation>
      <data src="http://www/mesodata.cgi?latest.mdf"
        param="RELH"/>
    /observation>
         
  </map>
</WxML>

In this example, all three map elements refer to the same data source, but with different refresh rates. The source will be reloaded from the server every 60 seconds, as specified by the smallest refresh rate. The first contour plot will be updated using the refreshed data source every 60 seconds, the second contour plot will be updated only every 5 minutes, and the observation plot will never be updated.

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